Solution rheology of kappa-carrageenan in the ordered and disordered conformations

In sight the behavior of natural Bletilla striata polysaccharide hydrocolloids by molecular dynamics method

Plant polysaccharides, distinguished by diverse glycosidic bonds and various cyclic sugar units, constitute a subclass of primary metabolites ubiquitously found in nature. Contrary to common understanding, plant polysaccharides typically form hydrocolloids upon dissolution in water, even though both excessively high and low temperatures impede this process. Bletilla striata polysaccharides (BSP), chosen for this kinetic study due to their regular repeating units, help elucidate the relationship between polysaccharide gelation and temperature. It is suggested that elevated temperatures enhance the mobility of BSP molecular chains, resulting in a notable acceleration of hydrogen bond breakage between BSP and water molecules and consequently, compromising the conformational stability of BSPs to some extent. This study unveils the unique relationship between polysaccharide dissolution processes and temperature from a kinetics perspective. Consequently, the conclusion provides a dynamical basis for comprehending the extraction and preparation of natural plant polysaccharide hydrocolloids, pharmaceuticals and related fields.

DSC and TMA Studies of Polysaccharide Physical Hydrogels

Various kinds of polysaccharides found in a wide variety of plants, bacteria, crustaceans and insects form hydrogels via physical aggregation in aqueous media. The major mass of hydrogels is water filled, ca. 95 - 99.5%, in a network structure, although the solid shape of the gel is maintained. In this paper, firstly the wide range of gelation mechanisms are briefly described, and then the thermal analysis of representative gel-forming polysaccharides, such as carrageenan, alginate, galactomannan, and pectin, is introduced. By differential scanning calorimetry (DSC), gel-sol and the sol-gel transition temperature of thermoreversible hydrogels are measured and phase diagram is established. It is suggested that binary systems showing sinusoidal gel-sol-gel transition are capable of being assembled. By thermomechanical analysis (TMA), the dynamic modulus (E') at around 1 × 10⁴ Pa of thermo-irreversible hydrogels was obtained using a sample holder designed to measure the viscoelastic properties in water. Reliable coordination is shown between the results obtained by DSC and TMA. In this review, the current research and several topics on concerning the thermal properties of polysaccharide physical hydrogels are introduced.

Primary, Secondary, Tertiary and Quaternary Structure Levels in Linear Polysaccharides: From Random Coil, to Single Helix to Supramolecular Assembly

Polysaccharides are ubiquitous in nature and represent an essential class of biopolymers with multiple levels of conformation and structural hierarchy. However, a standardized structural nomenclature, as in the case of proteins, is still lacking due to uncertainty on their hierarchical organization. In this work we use carrageenans as model polysaccharides to demonstrate that several structural levels exist and can be unambiguously resolved by statistical analysis on high resolution Atomic Force Microscopy images, supported by spectroscopic, X-ray scattering and rheological techniques. In direct analogy with proteins, we identify primary, secondary, tertiary and quaternary structures. The structure-property relationship induced by monovalent ions for κ-, ι- and the non-gelling control λ-carrageenan is established from the single chain regime to the occurrence of hydrogels at higher concentrations. For κ-carrageenan in the presence of potassium, a disorder-order transition from random coil to single helix is first observed (secondary structure), followed by intrachain supercoiling events (tertiary structure) and macroscopic anisotropic domains which are parts of a network (quaternary structure) with tunable elasticity up to ∼10³ Pa. In contrast, κ-carrageenan in the presence of sodium only produces changes in secondary structure without supercoiling events, prior to formation of gels, highlighting the ion-specificity of the process. Loosely intertwined single helices are observed for ι-carrageenan in the presence of sodium and potassium chloride, providing an elastic mesh with many junction zones, while λ-carrageenan does not undergo any structural change. A generality of the observed behavior may be inferred by extending these observations to a distinct class of polysaccharides, the weak carboxylic polyelectrolyte Gellan gum. These results advance our understanding of ion-specific structural changes of polysaccharides and the physical mechanisms responsible for their gelation.

Mapping the Complex Phase Behaviors of Aqueous Mixtures of κ-Carrageenan and Type B Gelatin

We report a detailed and complete phase diagram for an aqueous mixture of oppositely charged gelling biopolymers, type B gelatin and κ-carrageenan (KC) at pH 7.0. The phase diagram is studied in the ionic strength-temperature coordinate by means of turbidity, rheological and differential scanning calorimetric measurements, and macroscopic phase compositional analysis. Seven phase regions are identified, including (I) compatible region, (II) electrostatically induced associative phase separation (EIAPS) region, (III) hydrogen bonding induced associative phase separation (HBIAPS) region, (IV) coexistence of EIAPS and HBIAPS, (V) segregative phase separation (SPS) region, (VI) coexistence of HBIAPS and SPS, and (VII) SPS trapped by gelation. The HBIAPS reported for the first time here is attributed to the extensive hydrogen bonding formation between gelatin and KC above their conformational transition temperatures, as probed by addition of urea and methylene blue as well as by 2D (1)H-(1)H NOESY NMR. NaCl is found to have dual effects on HBIAPS. The electrostatic complexation at lower ionic strength facilitates the formation of hydrogen bonds between gelatin and KC and hence the HBIAPS. It is believed that the local structural arrangement of gelatin molecules or the change in local solvent environment prior to triple helix formation during cooling enables the formation of hydrogen bonds with KC.

Unravelling secondary structure changes on individual anionic polysaccharide chains by atomic force microscopy

The structural conformations of the anionic carrageenan polysaccharides in the presence of monovalent salt close to physiological conditions are studied by atomic force microscopy. Iota-carrageenan undergoes a coil-helix transition at high ionic strength, whereas lambda-carrageenan remains in the coiled state. Polymer statistical analysis reveals an increase in persistence length from 22.6±0.2 nm in the random coil, to 26.4±0.2 nm in the ordered helical conformation, indicating an increased rigidity of the helical iota-carrageenan chains. The many decades-long debated issue on whether the ordered state can exist as single or double helix, is conclusively resolved by demonstrating the existence of a unimeric helix formed intramolecularly by a single polymer chain.

Elucidation of release characteristics of highly soluble drug trimetazidine hydrochloride from chitosan-carrageenan matrix tablets

The aim of this study was to better understand the underlying drug release characteristics from matrix tablets based on the combination of chitosan (CS) and different types of carrageenans [kappa (κ)-CG, iota (ι)-CG, and lambda (λ)-CG]. Highly soluble trimetazidine hydrochloride (TH) was used as a model drug. First, characteristics of drug release from different formulations were investigated, and then in situ complexation capacity of CG with TH and CS was studied by differential scanning calorimetry and Fourier transform infrared spectroscopy. Erosion and swelling of matrix were also characterized to better understand the drug-release mechanisms. Effects of pH and ionic strength on drug release were also studied. It was found that not only ι-CG and λ-CG could reduce the burst release of TH by the effect of TH-CG interaction, CS-ι-CG- and CS-λ-CG-based polyelectrolyte film could further modify the controlled-release behavior, but not CS-κ-CG. High pH and high ionic strength resulted in faster drug release from CS-κ-CG- and CS-ι-CG-based matrix, but drug release from CS-λ-CG-based matrix was less sensitive to pH and ionic strength. In conclusion, CS-λ-CG-based matrix tablets are quite promising as controlled-release drug carrier based on multiple mechanisms.

Why inhaling salt water changes what we exhale

We find that inhaling salt water diminishes subsequently exhaled biomaterial in man and animals due to reversible stabilization of the airway lining fluid (ALF)/air interface as a novel potential means for control of the spread of airborne infectious disease. The mechanism of this phenomenon relates to charge shielding of mucin or mucin-like macromolecules that consequently undergo gelation; this gelation alters the physical properties of the ALF surface and reduces its breakup. Cations in the nebulized solution and apparent surface viscoelasticity of the ALF (more than any other ALF intrinsic physical property) appear to be responsible for the reduced tendency of the ALF to disintegrate into very small droplets. We confirm these effects in vivo and show their reversibility through nebulization of saline solutions to anesthetized bull calves.

K+ and Na+ effects on the gelation properties of κ-Carrageenan

The effects of K(+), Na(+) ions and their mixture on the conformational transition and macroscopic gel properties of kappa-Carrageenan system have been studied using different experimental techniques. The macroscopic gelation properties of kappa-Carrageenan were found to be dependent upon cosolute type. Indeed, a more ordered and strong gel was obtained in the presence of K(+) with respect to Na(+) ions. The gel properties obtained using mixtures of two cosolutes are shown to depend on the [K(+)]/[Na(+)] ratio.

Responsive hydrogels from the intramolecular folding and self-assembly of a designed peptide

A general peptide design is presented that links the pH-dependent intramolecular folding of beta-hairpin peptides to their propensity to self-assemble, affording hydrogels rich in beta-sheet. Chemical responsiveness has been specifically engineered into the material by linking intramolecular folding to changes in solution pH, and mechanical responsiveness, by linking hydrogelation to self-assembly. Circular dichroic and infrared spectroscopies show that at low pH individual peptides are unstructured, affording a low-viscosity aqueous solution. Under basic conditions, intramolecular folding takes place, affording amphiphilic beta-hairpins that intermolecularly self-assemble. Rheology shows that the resulting hydrogel is rigid but is shear-thinning. However, quick mechanical strength recovery after cessation of shear is observed due to the inherent self-assembled nature of the scaffold. Characterization of the gelation process, from the molecular level up through the macroscopic properties of the material, suggests that by linking the intramolecular folding of small designed peptides to their ability to self-assemble, responsive materials can be prepared. Cryo-transmission electron and laser scanning confocal microscopies reveal a water-filled porous scaffold on both the nano- and microscale. The environmental responsiveness, morphology, and peptidic nature make this hydrogel a possible material candidate for biomedical and engineering technology.